Lucas, S.G. and Spielmann, J.A., eds., 2007, The Global Triassic. New Mexico Museum of Natural History and Science Bulletin 41. 201 THE CONTINENTAL TETRAPOD-BEARING TRIASSIC OF SOUTH BRAZIL MAX C. LANGER1, ANA M. RIBEIRO2, CESAR L. SCHULTZ3 AND JORGE FERIGOLO2 1 Depto. Biologia, FFCLRP-USP, Av. Bandeirantes 3900, Ribeirão Preto, Brazil; e-mail: [email protected]; 2 Museu de Ciências Naturais, FZB-RS, Av. Salvador França 1427, Porto Alegre, Brazil; e-mail: [email protected], [email protected]; 3 Inst. Geociâncias, UFRGS, Av. Bento Gonçalves 9500, Porto Alegre, Brazil; e-mail [email protected] Abstract—The Rosário do Sul Group is one of the better-known tetrapod-bearing continental deposits of Triassic age. It crops out in central Rio Grande do Sul, south Brazil, and has yielded a fauna of more than 40 valid species, including temnospondyl, procolophonoideans, dicynodonts, cynodonts, sphenodontian, rhynchosaurs, and archosaurs. Its fossil record is herein briefly assessed, along with the stratigraphy of its bearing sequences. This includes the Early (perhaps earliest) Triassic Sanga do Cabral Formation, which correlates to the Lystrosaurus/ “Impoverished” zones of the Karoo Basin, and a second major stratigraphic sequence of Mid-Late Triassic age that broadly corresponds to the Santa Maria and Caturrita formations. The lower, cynodont-dicynodont dominated fauna of that sequence is partially Chañarian (Ladinian) in age, and encompasses the Dinodontosaurus Assem- blage-Zone. The Late Triassic fauna includes the Hyperodapedon and Ictidosaur assemblage-zones. The former, dominated by rhynchosaurs, includes some of the oldest known dinosaurs, and can be given an Ischigualastian (Carnian) age. The younger fauna contains advanced cynodonts and procolophonids, as well sphenodontians, most probably corresponding to the latest Triassic. INTRODUCTION The Rosário do Sul Group, and especially the Santa Maria Forma- tion within it, are well known for their tetrapod record. These Triassic deposits crop out along a 500 km belt in the south-central portion of Rio Grande do Sul, south Brazil (Fig. 1). Fossil tetrapods are, however, not restricted to the Santa Maria Formation, but also abound in the Sanga do Cabral and Caturrita formations, which respectively lay below and above that stratigraphic unit (Andreis et al., 1980). Ages attributed to the Rosário do Sul Group are mainly based on biostratigraphic studies of its tetrapod assemblages, and extend for most of the Triassic, with evidence of Induan- Olenekian (Cisneros and Schultz, 2002), Anisian (Abdala and Sá-Teixeira, 2004), Ladinian (Abdala et al., 2001), Carnian (Langer, 2005a) and Norian (Rubert and Schultz, 2004) faunas. This contribution includes a review of the fossil tetrapod record of the Rosário do Sul Group. Firstly, this is assessed according to the phylogenetic affinities of the valid taxa (Tables 1, 2), which are discussed based on most recent revisions of their taxonomic status. Thereafter, a second approach is taken, and current knowledge on the depositional sequences of the Rosário do Sul Group is used to order the fossil record of different sites in a stratigraphic framework. Finally, data on sequence stratigraphy of fossil-bearing deposits and phylogeny of fossil taxa are assembled to produce an as comprehensive as possible view of the faunal evolution of the South Brazilian Triassic. Institutional abbreviations: MCN, Museu de Ciências Naturais, Fundação Zoobotânica do Rio Grande do Sul; UFRGS, Instituto de Geociências, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brasil. These are indicated only if there is no bibliographic reference to the specimen/taxon in question. FOSSIL RECORD FIGURE 1. A, Map of the Paraná Basin (gray) in east-central South America, showing the location of Rio Grande do Sul, in south Brazil. B, Map of Rio The fossil biota of the Rosário do Sul Group includes a minimum Grande do Sul depicting the outcrop belt of the Rosario do Sul Group (based of 45 formally proposed, and valid tetrapod species: one temnospondyl, on DaRosa, 2005; DaRosa and Faccini, 2005). four procolophonoideans, three dicynodonts, 15 cynodonts, one sphenodontian, five rhynchosaurs, and 16 archosaurs. The picture is, Temnospondyli however, rather different in terms of abundance. Azevedo et al. (1990) quantified the fossil record of the Santa Maria Formation, where Lavina and Barberena (1985) assigned fragmentary temnospondyl dicynodonts represent about 60% of the specimens collected in most remains from the Sanga do Cabral Formation to the Lydekkerinidae and Middle Triassic assemblages, while rhynchosaurs account for about 90% Rhytidosteidae, but these have been recently reviewed by Dias-da-Silva in those of Carnian age. Other faunas are, conversely, dominated by et al. (2005, see also Dias-da-Silva, 2003), and referred to either cynodonts (Abdala et al., 2001). Rhytidosteidae or Temnospondyli incertae sedis. More complete mate- 202 TABLE 1. Fossil record presented by monophyletic hierarchy of Temnospondyli, Procolophonoidea, and Therapsida in the Rosário do Sul Group, Triassic of Rio Grande do Sul, Brazil. rial includes a partial mandible (Dias-da-Silva, 1998) and skull. The latter Parareptilia was described by Dias-da-Silva et al. (2006a) as a new rhytidosteid, Sangaia lavinai (Dias-da-Silva and Marsicano, 2006). According to those In the Rosário do Sul Group, parareptiles are known based only authors, Sangaia is most closely related to the Indian form on procolophonoideans (sensu Lee, 1995), whereas the possible occur- Indobatrachops panchetensis, from the Panchet Formation, Induan of rence of a pareiasaur (Schultz and Dias-da-Silva, 1999; Lucas, 2002) was the Damodar Valley (Chatterjee and Roy-Chowdhury, 1974; Lucas, 1998). dismissed by Cisneros et al. (2005). Four taxa were described: Candelaria In addition to these records from the Sanga do Cabral Formation, frag- barbouri Price, 1947 (see also DaRosa et al., 2004a); Procolophon pricei mentary temnospondyl remains were also reported from the Santa Maria Lavina, 1983; Procolophon brasiliensis Cisneros and Schultz, 2002; and Formation (Richter, 2001). Soturnia caliodon Cisneros and Schultz, 2003. A further partial skull was 203 TABLE 2. Fossil record presented by monophyletic hierarchy of Sphenodontia, Rhynchosauria, Prolacertiformes, and Archosauria in the Rosário do Sul Group, Triassic of Rio Grande do Sul, Brazil. also referred to the genus Procolophon (Langer and Lavina, 2000, Dias- within Leptopleurinae (Cisneros, 2006). In addition, S. caliodon has da-Silva et al., 2006b), but without further detail. According to Cisneros been regarded by Cisneros (2006) as the sister taxon of Hypsognathus et al. (2004), Candelaria barbouri belongs to Owenettidae, and is the fenneri, from the Newark Supergroup, Norian-Rhaetian of the North sister taxon of “Owenetta” kitchingorum, from the Lystrosaurus Assem- American Atlantic Coast (Sues et al., 2000). blage Zone, Induan of the Karoo Basin, South Africa (Reisz and Scott, Dicynodontia 2002), whereas the other three taxa belong to the Procolophonidae (Cisneros, 2006): Procolophon species (Cisneros and Schultz, 2002; Dicynodonts have long been recognized in the Triassic of Rio Dias-da-Silva et al., 2006b) within Procolophoninae and S. caliodon Grande do Sul (Tupí-Caldas, 1936; Huene, 1942; Romer, 1943; Romer 204 and Price, 1944), and considered an important component of its biota et al., 1996), from the Ischigualasto Formation, Argentina. The described (Barberena, 1977; Bonaparte, 1982). Despite this, current knowledge taxa include six traversodontids, eight probainognathians, and a cynodont seems to indicate the presence of only three taxa: Stahleckeria potens of ambiguous affinities, Protheriodon estudianti (Bonaparte et al. 2006a). Huene, 1938; Dinodontosaurus pedroanum (Tupí-Caldas, 1933; gen. All these forms were recorded in the Santa Maria and Caturrita forma- Romer, 1943), and Jachaleria candelariensis (Araújo and Gonzaga, 1980; tions, whereas only fragmentary postcranial remains of non-mammalian gen. Bonaparte, 1970). The genus Chanaria was also reported in south cynodonts have been collected in the Sanga do Cabral Formation (Abdala Brazil (Araújo, 1981), but it seems to represent a subjective synonym of et al., 2002a). Dinodontosaurus (King, 1988). In addition, Peruzzo and Araújo- The formally described traversodontids include: Gompho- Barberena (1995) assigned a partial skull to Ischigualastia sp., a genus dontosuchus brasiliensis Huene, 1928 (see Hopson, 1985); Traversodon otherwise known only in the Ischigualasto Formation, Carnian of Argen- stahleckeri Huene, 1938 (see Barberena, 1981a); Massetognathus tina (Cox, 1965; Rogers et al., 1993). This material has been referred to ochagaviae Barberena, 1981b; Exaeretodon riograndensis Abdala, Stahleckeria potens by Lucas (2001), but for Vega-Dias (pers. com., Barberena and Dornelles, 2002; Santacruzodon hopsoni Abdala and January 2007) its current status is ambiguous (see also Vega-Dias and Ribeiro, 2003; and Luangwa sudamericana Abdala and Sá-Teixeira, 2004. Schwanke, 2004a). Even so, Lucas (2001; Lucas and Heckert, 2002) Additional records include the poorly known Exaeretodon major (Huene, proposed the occurrence of the genus Ischigualastia in Rio Grande do 1938), originally described as a member of the genus Traversodon (see Sul, based on the material originally referred to Jachaleria candelariensis. Huene, 1942; Barberena, 1974; Abdala et al., 2002b), and three unnamed Yet, a reassessment